1. Field of the Invention
The invention relates to tubing expansion. In particular, the invention relates to methods and apparatus for expanding tubing downhole.
2. Description of the Related Art
A significant recent development in the oil and gas exploration and production industry has been the introduction of expandable bore-lining tubing, that is tubing which may be run into a drilled bore and then expanded to a larger diameter. The tubing may take any appropriate form, including but not limited to casing, liner or sandscreen. Various methods have been proposed for expanding the tubing downhole, including the use of expansion cones or mandrels that are pushed or pulled through the tubing mechanically and\or fluid pressure driven. Alternatively, a rotary expander may be utilised, that is, a device including a number of rollers, each roller with an axis of rotation generally parallel to the tubing axis. The expander is rotated within the tubing with the rollers in rolling contact with the tubing inner surface. The rollers may define a fixed diameter, or may be mounted to permit radial movement.
Each expansion device has its own advantages and disadvantages. One disadvantage of using a fluid-driven expansion cone is that the cone, which of course describes a diameter larger than the tubing to be expanded, must be initially accommodated within a larger diameter section of the tubing, which those of skill in the art sometimes refer to as a “garage” or “launcher”. This launcher is provided at the lower end of the tubing, and the end of the launcher, beyond the cone, may be selectively sealed and then pressured-up to push the cone upwardly through the tubing. Of course, this larger diameter tubing section limits the dimensions of the minimum diameter restriction that the assembly, including the remainder of the smaller diameter tubing, may pass through while being run into the bore. To minimise this limiting effect, the wall thickness of the launcher may be thinner than the wall thickness of the tubing to be expanded. However, this reduces the strength of the tubing which forms the launcher, such that the launcher may be more susceptible to damage as the tubing is run into the bore, which would interfere with the ability to launch the cone. Furthermore, having a relatively thin wall reduces the ability of the launcher to withstand the elevated pressures which are required to drive the cone through the tubing.
It is among the objectives of embodiments of the present invention to obviate or mitigate these difficulties.